The present invention relates to a semiconductor laser device which contains no Al in its active region and whose oscillation wavelength is in a 780 nm band (i.e., larger than 760 nm and smaller than 800 nm). The invention also relates to an optical disk unit using the semiconductor laser device.
Semiconductor laser devices of the 780 nm band have been widely used as semiconductor laser devices for reproducing discs such as CDs (Compact Disks) and MDs (Mini Disks). Among others, a semiconductor laser device which exhibits high reliability even with 120 mW or higher power is keenly desired as a semiconductor laser device for use with CD-Rs (CD-Recordable's) capable of high-speed writing.
In the case of a conventional AlGaAs quantum well structure in which Al is contained in well layers and barrier layers, there is an issue that the reliability particularly at high temperatures or high power deteriorates. The reason of this is considered that Al, being an active substance, would react even with a trace quantity of impurities such as oxygen, thereby amplifying the deterioration of the material. A countermeasure for this could be that high power and high reliability are implemented by providing a structure in which Al is not contained in the well layer/barrier layer. However, actually, there has not yet been developed a semiconductor laser device that has enough reliability with 120 mW or higher power at the 780 nm band.
As semiconductor laser devices of an oscillation wavelength of 810 nm with a structure in which Al is not contained in the well layer/barrier layer, there have been proposed those disclosed in Japanese Patent Laid-Open Publication HEI 11-220224 and Japanese Journal of Applied Physics Vol. 38 (1999) pp. L387-L389.